Need to send in Trade-In device before OP12 delivers??

I just ordered OP12, and the estimated delivery is 26th Feb. Howevere, OnePlus has asked me to send the trade-in device by 24th of Feb. The trade in device is OP7pro and I am using it, how do I transfer the data before new phone delivers and what do I do in in-between days? Is OnePlus crazy? Shouldn't the trade in be after new phone is delivered, as Samsung does?